The present invention relates to a method and apparatus for detection of tumors, and particularly tumors in human breast tissue.
The purpose of any imaging system for breast cancer detection is to assist in the diagnosis of early stage breast cancer. Currently, women are encouraged to participate in breast cancer screening programs utilizing mammography. Mammograms are x-rays images of a compressed breast, and are acknowledged to be the leading method of breast imaging currently available. While mammography is very sensitive to lesions in the breast, it has acknowledged limitations. For example, mammograms create images of the breast based on density differences and there may be only a slight difference in density between normal tissue and tumors. This is especially problematic for imaging women with dense breasts, which comprise a significant portion of the population. Another limitation is that a lesion may not be immediately diagnosed via a single mammogram. Further investigation of suspicious areas involves additional mammography, ultrasound and, in some cases, biopsy. Less than 10% of the suspicious areas investigated are diagnosed as cancer.
Every time a mammogram is taken, the patient incurs a small risk of having a breast tumor induced by the ionizing radiation properties of the X-rays used during the mammogram. Also, the process is sometimes imprecise and, as a result, not cost-efficient. Accordingly, the National Cancer Institute has not recommended mammograms for women under fifty years of age, who are not as likely to develop breast cancers as are older women. However, while only about twenty two percent of breast cancers occur in women under fifty, data suggest that breast cancer is more aggressive in pre-menopausal women.
Mammograms require interpretation by radiologists who can spot cancers between five and ten millimeters in diameter, and the prognosis is excellent in those cases. However, about ten to fifteen percent of tumors of this size and most tumors below this size are not detected. One study showed major clinical disagreements for about one-third of the same mammograms that were interpreted by a group of radiologists. Further, many women find that undergoing a mammogram is a decidedly painful experience.
These limitations have generated interest in alternative breast imaging methods. Many medical imaging technologies have been applied to this problem, including ultrasound and magnetic resonance (“MR”) imaging. Ultrasound is often used to differentiate solid tumors from liquid cysts, but does not provide definitive information on whether a solid tumor is malignant or benign. MR imaging provides a map of the tissue distributions in the breast, and MR breast imaging usually involves injection of a contrast agent. The uptake and washout of the contrast agent in the vicinity of the suspicious lesion is monitored, however it may be difficult to provide a definitive diagnosis as malignancies generally do not have behavior that is consistently and distinctly different than benign lesions.
Therefore, there is a need in the art of medical imaging for a complementary breast imaging tool. Specifically, imaging tools that may be applied to women with suspicious mammograms to quickly and effectively indicate the presence or absence of a tumor would be of great value. The keys to a successful technology are the presence of a consistent contrast between normal breast tissues and malignant lesions, and a difference in the response of benign and malignant tissues. In other words, a physical basis for tumor detection must exist.
Microwave imaging for breast tumor detection is considered to be promising, as it is believed that there is a significant or detectable contrast in malignant, benign and normal tissues over a broad frequency range.